Control of flow or rheological properties of thermoplastic polyesters during processing, such as extrusion, molding, milling and forming into fibers, is necessary. The amount and type of additives employed for this purpose is dependent on the particular polyester used, the other compounding ingredients present in the formulation, the type of processing and the processing conditions.
Numerous additives for thermoplastic polyesters are known and used as flow promoters, friction reducers, release agents, parting agents, spinning aids and the like. For example, when processing polyester fibers ethoxylated fatty esters and emulsified polyethylene, natural and synthetic waxes or mineral oils can be used. Fatty amides or bisamides are also used as lubricating aids when polyesters are extruded. Stearic acid, metal stearates, mono- and dialkylphosphates and their metal soaps, and waxes such as carnauba and candellila, are also commonly used with polyesters in molding applications.
It would be highly desirable and advantageous if additives were available which could be easily incorporated into both fiber-forming and film-forming polyesters and copolyesters, such as poly(ethylene terephthalate), and the structural or engineering-type polyesters and copolyesters including poly(butylene terephthalate).